Lenses are in this case generally understood to be both refractive lenses and diffractive lenses (for example, Fresnel zone plates). A diaphragm provided with a small hole can also be provided with effective powers (effective refractive powers), as described with reference to the drawings. Optical elements with a zero nominal power but with a limited aperture such as, for example, circular or annular plates with parallel front and rear surfaces can therefore also be understood here as "lenses".
Different zones of a lens are represented by areas of a lens which can be differentiated by physical properties, wherein between the zones the physical properties alter very rapidly or abruptly over a relatively small area. In particular, step-like sudden changes in the thickness of the lens material being used, for example, steps on the front or rear surface of the lens, delimit different zones of a lens. The use of different lens materials in different areas of the lens also results in a zoned lens in the present sense. The geometrical arrangement of the different zones can be configured in many different ways. For example, a central circular zone can be provided, to which outer concentric annular zones are adjacent. The surface areas of the different zones can be the same or different.